My vote to close as too broad was simply due to the OP not identifying where in the US he would be traveling. While he chose not to identify his country of origin, I could reasonably hypothesize it is a Scandinavian country. (I say this because of his chosen identity spelling, with the fancy Scandinavian-ish O). I may be wrong, but in reality, it doesn't really matter. Chances are very good it is a European country, and one thing I learned many years ago, is that Europeans who have never traveled to the US simply do not comprehend its immensity. While Russia may be larger, one does not usually travel to Siberia.
As has been stated by others, there are many different states, each with it's own gun laws (and several cities with differing ones as well). Where I live is open carry (with licensed concealed carry). There are also a lot of Federal buildings and land here. Not many open-carry gun enthusiasts carry, nor openly. Many of my associates have licenses for concealed, however.
Where I was raised is also open-carry, and yes, you will see firearms everywhere. On belts, on gun racks, behind the doors, in shoulder holsters.
If you're here during the summer months, depending on where you are, you may also see a National Guard unit going to, or coming from "Summer Drill" carrying large weapons. All police officers carry. There are many armed guards in and around certain buildings.
Many other places you'll not see a single firearm.
All of what I have said, to me, simply adds up to "too broad to answer for everywhere every time. While you have said we should be able to "sum up for most of the US, that simply is not true. I believe you when you say you've visited many places in the US. I don't believe you noticed every person open carrying weapons. A properly carried weapon isn't noticed. I'm not talking about concealed carry either. I can wear my pistol, in its holster on my belt, and 99 out of 100 people won't ever even notice it.
What wasn't asked, nor answered, if I recall correctly, is that the original OP need not fear legal open-carriers. (I'm not saying he/she shouldn't fear them, because I cannot choose what he fears for him) I'm saying the people who choose to open-carry firearms legally, simply are not going to be the ones who may cause him harm. It's the criminals he needs fear, and they, by and large, do not open-carry until actively committing a crime.
So, you asked why, and that is my why. There are too many distinct laws and areas to be able to "sum up the entirety of the US" so that one single answer is correct, except to say just that: it depends where you will be visiting.
The last thing I would say here, is that a hold, or closure, does not mean the question will disappear, usually. If the OP would edit it to show where he intends to visit, I would be happy to be the first to Vote to Reopen.